serial: 8250: Handle case port doesn't have TEMT
From: Giulio Benetti <giulio.benetti@...> Date: Wed, 6 Jun 2018 11:51:52 +0200
Commit-Message
Some 8250 ports only have TEMT interrupt, so current implementation can't work for ports without it. The only chance to make it work is to loop-read on LSR register. With NO TEMT interrupt check if both TEMT and THRE are set looping on LSR register. Signed-off-by: Giulio Benetti <giulio.benetti@...> Signed-off-by: Heiko Stuebner <heiko.stuebner@...>
Patch-Comment
drivers/tty/serial/8250/8250.h | 2 +- drivers/tty/serial/8250/8250_of.c | 2 +- drivers/tty/serial/8250/8250_omap.c | 2 +- drivers/tty/serial/8250/8250_port.c | 30 +++++++++++++++++++++-------- include/linux/serial_8250.h | 1 + 5 files changed, 26 insertions(+), 11 deletions(-)
Statistics
- 26 lines added
- 11 lines removed
Changes
------------------------ drivers/tty/serial/8250/8250.h ------------------------
index 50a4c174410d..9e049d2a039e 100644
@@ -190,7 +190,7 @@ void serial8250_rpm_put(struct uart_8250_port *p);
void serial8250_rpm_get_tx(struct uart_8250_port *p);
void serial8250_rpm_put_tx(struct uart_8250_port *p);
+int serial8250_em485_init(struct uart_8250_port *p, bool has_temt_isr);
void serial8250_em485_destroy(struct uart_8250_port *p);
/* MCR <-> TIOCM conversion */
---------------------- drivers/tty/serial/8250/8250_of.c -----------------------
index 92fbf46ce3bd..c77ab44a5468 100644
@@ -64,7 +64,7 @@ static int of_8250_rs485_config(struct uart_port *port,
* are idempotent
*/
if (rs485->flags & SER_RS485_ENABLED) {
+ int ret = serial8250_em485_init(up, true);
if (ret) {
rs485->flags &= ~SER_RS485_ENABLED;
--------------------- drivers/tty/serial/8250/8250_omap.c ----------------------
index 836e736ae188..241322900298 100644
@@ -734,7 +734,7 @@ static int omap_8250_rs485_config(struct uart_port *port,
* are idempotent
*/
if (rs485->flags & SER_RS485_ENABLED) {
+ int ret = serial8250_em485_init(up, true);
if (ret) {
rs485->flags &= ~SER_RS485_ENABLED;
--------------------- drivers/tty/serial/8250/8250_port.c ----------------------
index 67aa3a2a9afa..3d1d8490bc42 100644
@@ -605,15 +605,17 @@ EXPORT_SYMBOL_GPL(serial8250_rpm_put);
/**
* serial8250_em485_init() - put uart_8250_port into rs485 emulating
* @p: uart_8250_port port instance
+ * @p: bool specify if 8250 port has TEMT interrupt or not
*
* The function is used to start rs485 software emulating on the
* &struct uart_8250_port* @p. Namely, RTS is switched before/after
* transmission. The function is idempotent, so it is safe to call it
* multiple times.
*
+ * If has_temt_isr is passed as true, the caller MUST enable interrupt
+ * on empty shift register before calling serial8250_em485_init().
+ * This interrupt is not a part of 8250 standard, but implementation
+ * defined.
*
* The function is supposed to be called from .rs485_config callback
* or from any other callback protected with p->port.lock spinlock.
@@ -622,7 +624,7 @@ EXPORT_SYMBOL_GPL(serial8250_rpm_put);
*
* Return 0 - success, -errno - otherwise
*/
+int serial8250_em485_init(struct uart_8250_port *p, bool has_temt_isr)
{
if (p->em485)
return 0;
@@ -639,6 +641,7 @@ int serial8250_em485_init(struct uart_8250_port *p)
p->em485->start_tx_timer.function = &serial8250_em485_handle_start_tx;
p->em485->port = p;
p->em485->active_timer = NULL;
+ p->em485->has_temt_isr = has_temt_isr;
serial8250_em485_rts_after_send(p);
return 0;
@@ -1475,11 +1478,22 @@ static inline void __stop_tx(struct uart_8250_port *p)
/*
* To provide required timeing and allow FIFO transfer,
* __stop_tx_rs485() must be called only when both FIFO and
+ * shift register are empty. If 8250 port supports it,
+ * it is for device driver to enable interrupt on TEMT.
+ * Otherwise must loop-read until TEMT and THRE flags are set.
*/
+ if (em485->has_temt_isr) {
+ if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
+ return;
+ } else {
+ int val;
+
+ if (serial_in_poll_timeout(p, UART_LSR, val,
+ (val & BOTH_EMPTY) != BOTH_EMPTY,
+ 100000) < 0)
+ pr_warn("%s: timeout waiting for fifos to empty\n",
+ p->port.name);
+ }
em485->active_timer = NULL;
------------------------- include/linux/serial_8250.h --------------------------
index bb2bc99388ca..c4b4469c272b 100644
@@ -79,6 +79,7 @@ struct uart_8250_em485 {
struct hrtimer start_tx_timer; /* "rs485 start tx" timer */
struct hrtimer stop_tx_timer; /* "rs485 stop tx" timer */
struct hrtimer *active_timer; /* pointer to active timer */
+ bool has_temt_isr; /* variant has TEMT interrupt */
struct uart_8250_port *port; /* for hrtimer callbacks */
};